Process for the production of iron oxide fine powder

Abstract

A process for producing iron oxide fine powder of high purity from an oxide iron ore such as hematite or magnetite by only physical processing is disclosed, which comprises the steps of: providing a preliminarily ground raw material powder of an oxide iron ore or a mixture thereof having the impurity content in a specific range; classifying the raw material iron ore powder under such conditions that fine particles smaller than 10 mu m in diameter are removed from the ore powder; optionally treating the classified powder with an acid solution; refining the classified, optionally acid-treated iron ore powder by means of gravity concentration; and finish grinding the refined powder to reduce the particle size to a desired level.

What is claimed is: 
     
       1. A process for producing iron oxide fine powder of high purity from an oxide iron ore, comprising the steps of: (a) providing as a raw material an oxide iron ore or a mixture thereof in the form of preliminarily ground powder in which the total amount of metal oxide impurities having a specific gravity between 4.5 and 5.5 and/or being capable of forming an iron compound with an iron oxide present in the raw material is not greater than 1.5% by weight based on the total weight of iron oxides present therein;   (b) subjecting the iron ore powder to classification under such conditions that fine particles smaller than 10 μm in diameter are removed from the ore powder;   (c) refining the ore powder by means of gravity concentration; and   (d) finish grinding the refined powder to reduce the particle size to a desired level.   
     
     
       2. The process according to claim 1 wherein the total amount of metal oxide impurities having a specific gravity between 4.5 and 5.5 and/or being capable of forming an iron compound with an iron oxide present in the raw material is not greater than 1.3% by weight based on the total weight of iron oxides present therein. 
     
     
       3. The process according to claim 1 wherein the content of iron oxides in the raw material is at least 90% by weight. 
     
     
       4. The process according to claim 1 wherein the average particle size of the preliminarily ground raw material is in the range of from 20 to 200 μm. 
     
     
       5. The process according to claim 1 wherein the raw material is selected from hematite, magnetite, and a mixture thereof. 
     
     
       6. The process according to claim 5 wherein the raw material is hematite. 
     
     
       7. The process according to claim 1 wherein the powder obtained by the classification in step (b) contains up to 15% by weight of fine particles smaller than 10 μm in diameter. 
     
     
       8. The process according to claim 7 wherein the powder obtained by the classification in step (b) contains up to 5% by weight of fine particles smaller than 10 μm in diameter. 
     
     
       9. The process according to claim 1 wherein the classification in step (b) is carried out under such conditions that coarse particles greater than 250 μm in diameter are also removed in addition to fine particles smaller than 10 μm in diameter. 
     
     
       10. The process according to claim 1 wherein the refining in step (c) is carried out by means of either table concentration or flotation, or a combination of both. 
     
     
       11. The process according to claim 1 wherein the classified raw material powder obtained in step (b) is subjected to acid treatment by dipping the powder in an acid solution prior to or during the refining in step (c). 
     
     
       12. The process according to claim 11 wherein the acid solution has a pH of not greater than 5. 
     
     
       13. The process according to claim 11 wherein the acid solution has a pH of not greater than 4. 
     
     
       14. The process according to claim 11 wherein the acid treatment is carried out in the presence of one or more flotation agents with agitation. 
     
     
       15. The process according to claim 11 wherein the acid treatment is carried out, after which the powder is refined by table concentration. 
     
     
       16. The process according to claim 1 wherein the iron oxide fine powder product contains at least 98.5% by weight iron oxide. 
     
     
       17. The process according to claim 16 wherein the SiO 2  and Al 2  O 3  contents of the iron oxide fine powder product are not greater than 0.3% and not greater than 0.1% by weight, respectively. 
     
     
       18. The process according to claim 1 wherein the iron oxide fine powder product obtained after the finish grinding in step (d) has an average particle size suitable for use in the manufacture of ferrite magnets. 
     
     
       19. The process according to claim 18 wherein the average particle size of the iron oxide product is in the range of from 0.5 to 5.0 μm, and preferably in the range of from 0.8 to 2.0 μm. 
     
     
       20. A process for producing iron oxide fine powder of high purity from a hematite ore, comprising the steps of: (a) providing a hematite ore raw material in the form of preliminarily ground powder in which the total amount of metal oxide impurities having a specific gravity between 4.5 and 5.5 and/or being capable of forming an iron compound with an iron oxide present in the raw material is not greater than 1.5% by weight based on the total weight of iron oxides present therein;   (b) subjecting the hematite powder to classification under such conditions that fine particles smaller than 10 μm in diameter are removed from the hematite powder;   (c) refining the ore powder by means of gravity concentration; and   (d) finish grinding the refined powder to reduce the particle size to a desired level.   
     
     
       21. A process for producing iron oxide fine powder of high purity from an oxide iron ore, comprising the steps of: (a) providing as a raw material an oxide iron ore or a mixture thereof in the form of preliminarily ground powder in which the total amount of metal oxide impurities having a specific gravity between 4.5 and 5.5 and/or being capable of forming an iron compound with an iron oxide present in the raw material is not greater than 1.5% by weight based on the total weight of iron oxides present therein;   (b) subjecting the iron ore powder to classification under such conditions that fine particles smaller than 10 μm in diameter are removed from the ore powder;   (c) treating the ore powder with an acid solution of pH 5 or below prior to or during the subsequent refining step;   (d) refining the ore powder by means of gravity concentration; and   (e) finish grinding the refined powder to reduce the particle size to a desired level.   
     
     
       22. The process according to claim 21 wherein the acid treatment in step (c) is carried out in the presence of one or more flotation agents with agitation. 
     
     
       23. The process according to claim 21 wherein the pH of the acid solution is 4 or below. 
     
     
       24. The process according to claim 21 wherein after the acid treatment in step (c) the powder is refined by table concentration in step (d).